In the fanfiction, Naruto could uncover a secret cloning technology in the lab. This could be related to Orochimaru's experiments but on a much larger scale. There might be clones of powerful ninjas stored in the lab for some evil purpose. Naruto would then have to deal with the implications of this discovery, whether it's stopping the clones from being released or finding a way to use this technology for good. Also, he might find a secret passage in the lab that leads to an even more mysterious place filled with more secrets waiting to be discovered.
He might uncover a hidden weapon that could change the balance of power in the ninja world.
One secret could be the formula for a super - strong chakra - enhancing potion. This would give him an edge in battles against tough opponents.
He could uncover the truth about his father's real mission before he died. Maybe it was something that was kept hidden from the village for some reason.
I'm not entirely sure about all the secrets in the Snow Child Secret Story in Maplestory. But generally, it might involve some special quests related to the snow child character. Maybe it has to do with a unique item or power that the snow child possesses.
He could uncover secrets about his family. There might be some hidden records in the library that reveal things about his father or mother that he never knew before.
The lab could hold secrets about Orochimaru's past. Maybe there are records of his early days as a ninja, his training, and what led him to become so obsessed with immortality. Naruto might stumble upon these records and gain a better understanding of his enemy.
It could also be Kakashi. There might be fanfictions where he has some secrets related to Naruto. For instance, he might be aware of a secret mission related to Naruto that he has been keeping from everyone, which could be a major plot point in the fanfiction.
It could be secrets about a character's past, like a hidden identity or a past crime they committed.
Sasuke could be one of the characters aware of Naruto's secrets. Given their intense rivalry and deep friendship, Sasuke might have noticed something odd about Naruto and dug deeper to find out. Maybe Naruto let something slip during one of their battles or emotional conversations.
Ino could uncover Naruto's insecurities about his own abilities. Despite his confident exterior, Naruto might have doubts in his mind about whether he's truly strong enough to protect the village and his friends. Ino might then use this knowledge to encourage him and boost his confidence.
In this fanfiction, Naruto might reveal his insecurities about being the Jinchuriki at first. He could share how he was really scared of the Nine - Tails inside him and how he had to constantly battle with the fear of losing control.